The agencies say their needs are too different and that manufacturers are not yet ready to build trains that can run on both Amtrak's 100-year-old rail lines and the high-speed corridors planned for California.

The agencies had hoped to reduce costs and lure manufacturers to build the trains in the United States by bidding jointly.

But high-speed rail spokeswoman Lisa-Marie Alley says it became clear in meetings over the last few weeks that the requirements were too different.